Aircraft manufacturers are intensively occupied by efforts to increase the passenger transport capacity of passenger aircraft, due to the ever-increasing volume of air passenger traffic. Thus, large capacity aircraft have become known, in which the space of several decks arranged one above another can be utilized for passenger cabin space and service facilities. For example, German Patent Publication 4,116,524 describes an aircraft having not only an upper and a main deck, but also a lower deck having a floor adjacent the fuselage belly. This lower deck is also to be used by passengers Thus, in addition to the freight containers arranged in a portion of the lower deck, modules are also provided which enclose sleeping cabins or other passenger cabins, for example, having seating arrangements and/or service facilities such as service galleys or restrooms installed therein.
Disadvantageously, however, the passenger modules provided on the lower deck according to the prior art can only be used by passengers during the cruise flight portion of a flight, and not during take-off and landing phases of a flight. The use of such a lower deck by passengers during take-off and landing has been prohibited by strict regulations regarding passenger safety in the event of a crash or emergency landing of the aircraft. A substantial disadvantage of the prior art provision of passenger modules on a lower deck is seen in that the lower deck cannot be used by the passengers at all times during a flight. Thus, the total passenger capacity of the aircraft is not effectively increased, but rather remains limited to the seating capacity of the main passenger decks during the take-off and landing. The prior art arrangements of aircraft decks suffer this disadvantage because it has not been suggested how to provide sufficient safety for the passengers in the lower deck during the take-off and landing phase of a flight, especially because the impact energy of a crash or emergency landing of an aircraft was substantially only absorbed by deformation of the lower fuselage structure, namely the fuselage belly. In the case of a crash or emergency landing, the fuselage belly and the underfloor structure of a lower deck collapses upward, whereby hardly any space remains within the lower deck to allow survival of the passengers. Serious injury and death of the passengers cannot be avoided. For this reason, it has not previously been possible to provide a lower deck that can be continuously occupied by passengers and passenger service facilities during all phases of a flight.